Molecular strategies are being developed to modulate unwanted gene expression that either directly causes, participates in, or aggravates a disease state. One such strategy involves inhibiting gene expression with oligonucleotides complementary in sequence to the messenger RNA of a deleterious target gene. The messenger RNA strand is a copy of the coding DNA strand and is therefore, as the DNA strand, called the sense strand. Oligonucleotides that hybridize to the sense strand are called antisense oligonucleotides. Binding of these strands to mRNA interferes with the translation process and consequently with gene expression.
Certain nucleotide-based compounds have been utilized in various therapeutic applications. In particular, various oligonucleotides have been investigated including single-stranded and double-stranded oligonucleotides, and analogues. To be useful in in vivo applications, an oligonucleotide must have a plethora of properties including the ability to penetrate a cell membrane, have good resistance to extra- and intracellular nucleases, have high affinity and specificity for the target and preferably have the ability to recruit endogenous enzymes such as RNAseH, RNAaseIII, RNAseL etc.
A fundamental property of oligonucleotides that underlies many of their potential therapeutic applications is their ability to recognize and hybridize specifically to complementary single stranded nucleic acids employing either Watson-Crick hydrogen bonding (A-T and G-C) or other hydrogen bonding schemes such as the Hoogsteen/reverse Hoogsteen mode. Affinity and specificity are properties commonly employed to characterize hybridization characteristics of a particular oligonucleotide. Affinity is a measure of the binding strength of the oligonucleotide to its complementary target (expressed as the thermostability (Tm) of the duplex). Each nucleobase pair in the duplex adds to the thermostability and thus affinity increases with increasing size (number of nucleobases) of the oligonucleotide. Specificity is a measure of the ability of the oligonucleotide to discriminate between a fully complementary and a mismatched target sequence.
Modified nucleic acids are known to be used to improve for example stabilisation of the oligonucleotides, in particular for the gapmer designs, such as when 1 or more modified nucleotides are present in either or both of the wing regions. Examples of modifications include 2′-O-alkyl-RNA units, 2′-amino-DNA units, 2′-fluoro-DNA units, LNA units, arabino nucleic acid (ANA) units, 2′-fluoro-ANA units, HNA units, INA (intercalating nucleic acid—Christensen, 2002. Nucl. Acids. Res. 2002 30: 4918-4925, hereby incorporated by reference) units, 2′MOE units, ENA (ethylene nucleic acid), UNA (Unlocked Nucleic Acid, Fluiter et al., Mol. Biosyst., 2009, 10, 1039), Tricyclo DNA (R. Steffens & C. J. Leumann, J. Am. Chem. Soc, 1997, 119, 11548-49), cET-LNA (shown herein), and LNA. FIG. 4 presents drawings of some of these analogues.
A particular efficacious modified nucleic acid is referred to as a Locked Nucleic Acids (LNA). LNAs have been reported in the art—for example see International Patent Application WO 99/14226; P. Nielsen et al, J. Chem. Soc., Perkin Trans. 1, 1997, 3423; P. Nielsen et al., Chem. Commun., 1997, 9, 825; N. K. Christensen et al., J. Am. Chem. Soc., 1998, 120, 5458; A. A. Koshkin et al., J. Org. Chem., 1998, 63, 2778; A. A Koshkin et al. J. Am. Chem. Soc. 1998, 120, 13252-53; Kumar et al. Bioorg, & Med. Chem. Lett., 1998, 8, 2219-2222; and S. Obika et al., Bioorg. Med. Chem. Lett., 1999, 515. Interestingly, incorporation of LNA units containing a 2′-O,4′-C-methylene bridge into an oligonucleotide sequence leads to an unprecedented improvement in the hybridization stability of the modified oligonucleotide (see above and e.g., S. K. Singh et al., Chem. Commun, 1998, 455). Oligonucleotides comprising the 2′-O,4′-C-methylene bridge (LNA) units and also the corresponding 2′-thio-LNA (thio-LNA), 2′-HN-LNA (amino-LNA), and 2′-N(R)-LNA (amino-R-LNA) analogue, form duplexes with complementary DNA and RNA with thermal stabilities not previously observed for bi- and tricyclic nucleosides modified oligonucleotides. The increase in Tm per modification varies from +3 to +11° C., and furthermore, the selectivity is also improved. No other DNA analogue has reproducibly shown such high affinity for nucleic acids.
In a particular aspect, the present invention relates to hepatitis B virus (HBV) therapies. Hepatitis B is a viral disease caused by the hepatitis B virus (HBV). It is transmitted parenterally by contaminated material such as blood and blood products, contaminated needles, sexually and vertically from infected or carrier mothers to their offspring. In those areas of the world where the disease is common vertical transmission at an early age results in a high proportion of infected individuals becoming chronic carriers of hepatitis B. It is estimated by the World Health Organization that more than 2 billion people have been infected worldwide, with about 4 million acute cases per year, 1 million deaths per year, and 350-400 million chronic carriers. Approximately 25% of carriers die from chronic hepatitis, cirrhosis, or liver cancer and nearly 75% of chronic carriers are Asian. Hepatitis B virus is the second most significant carcinogen behind tobacco, causing from 60% to 80% of all primary liver cancer. HBV is 100 times more contagious than HIV.
The hepatitis B virus (HBV) is an enveloped, partially double-stranded DNA virus. The compact 3.2 kb HBV genome consists of four overlapping open reading frames (ORF), which encode for the core, polymerase (Pol), envelope and X-proteins. The Pol ORF is the longest and the envelope ORF is located within it, while the X and core ORFs overlap with the Pol ORF. The lifecycle of HBV has two main events: 1) generation of closed circular DNA (cccDNA) from relaxed circular (RC DNA), and 2) reverse transcription of pregenomic RNA (pgRNA) to produce RC DNA. Prior to the infection of host cells, the HBV genome exists within the virion as RC DNA. It has been determined that HBV virions are able to gain entry into host cells by non-specifically binding to the negatively charged proteoglycans present on the surface of human hepatocytes and via the specific binding of HBV surface antigens (HBV sAg). Once the virion has entered the cell, the viral cores and the encapsidated RC DNA are transported by host factors, via a nuclear localization signal, into the nucleus through the Impβ/Impα nuclear transport receptors. Inside the nucleus, host DNA repair enzymes convert the RC DNA into cccDNA. cccDNA acts as the template for all viral mRNAs and as such, is responsible for HBV persistence in infected individuals. The transcripts produced from cccDNA are grouped into two categories; pgRNA and subgenomic RNA. Subgenomic transcripts encode for the three envelope (L, M and S) and X proteins, and pgRNA encodes for Pre-Core, Core, and Pol proteins. Inhibition of HBV gene expression or HBV RNA synthesis leads to the inhibition of HBV viral replication and antigens production. For instance, IFN-α was shown to inhibit HBV replication and viral HBsAg production by decreasing the transcription of pregenomic RNA (pgRNA) and subgenomic RNA from the HBV covalently closed circular DNA (cccDNA) minichromosome. All HBV viral mRNAs are capped and polyadenylated, and then exported to the cytoplasm for translation. In the cytoplasm, the assembly of new virons is initiated and nascent pgRNA is packaged with viral Pol so that reverse transcription of pgRNA, via a single stranded DNA intermediate, into RC DNA can commence. The mature nucleocapsids containing RC DNA are enveloped with cellular lipids and viral L, M, and S proteins and then the infectious HBV particles are then released by budding at the intracellular membrane. Interestingly, non-infectious particles are also produced that greatly outnumber the infectious virions. These empty, enveloped particles (L, M and S), are referred to as subviral particles. Importantly, since subviral particles share the same envelope proteins and as infectious particles, it has been surmised that they act as decoys to the host immune system and have been used for HBV vaccines. The S, M, and L envelope proteins are expressed from a single ORF that contains three different start codons. All three proteins share a 226aa sequence, the S-domain, at their C-termini. M and L have additional pre-S domains, Pre-S2 and Pre-S2 and Pre-S1, respectively. However, it is the S-domain that has the HBsAg epitope.
Hepatitis B viral infections are a continuing medical problem because, like any rapidly-replicating infectious agent, there are continuing mutations that help some sub-populations of HBV become resistant to current treatment regimens. Currently the recommended therapies for chronic HBV infection by the American Association for the Study of Liver Diseases (AASLD) and the European Association for the Study of the Liver (EASL) include interferon alpha (INFa), pegylated interferon alpha-2a (Peg-IFN2a), entecavir, and tenofovir. However, typical interferon therapy is 48-weeks and results in serious and unpleasant side effects, and HBeAg seroconversion, 24 weeks after therapy has ceased, ranges from only 27-36%. Seroconversion of HBsAg is even lower—only 3% observed immediately after treatment ceases, with an increase to upwards of 12% after 5 years.
The secretion of antiviral cytokines in response to HBV infection by the hepatocytes and/or the intra-hepatic immune cells plays a central role in the viral clearance of infected liver. However, chronically infected patients only display a weak immune response due to various escape strategies adopted by the virus to counteract the host cell recognition systems and the subsequent antiviral responses.
Many observations showed that several HBV viral proteins could counteract the initial host cellular response by interfering with the viral recognition signaling system and subsequently the interferon (IFN) antiviral activity. Among these, the excessive secretion of HBV empty subviral particles (SVPs, HBsAg) may participate to the maintenance of the immunological tolerant state observed in chronically infected patients (CHB). In particular, SVPs could contribute to the absence of antigen presentation by dendritic cells together with the lack of HBV-specific T cell immune activation to enable viral persistence. HBsAg quantification is a significant biomarker to predict the infection outcome; however the achievement of HBsAg seroconversion is rarely observed in chronically infected patients. The reduction of the SVP and HBsAg burden is thought as a pathway to recover anti-viral immune function and the seroconversion to HBsAg-negative after antiviral therapy can be seen as an indication as a functional cure and remains the ultimate goal of therapy. Therefore, targeting HBV gene expression leading to reduction of HBsAg together with HBV DNA levels in CHB patients may significantly improve CHB patient immune reactivation and remission.
The nucleoside and nucleotide therapies entecavir and tenofovir are successful at reducing viral load, but the rates of HBeAg seroconversion and HBsAg loss are even lower than those obtained using IFNa therapy. Other similar therapies, including lamivudine (3TC), telbivudine (LdT), and adefovir are also used, but for nucleoside/nucleotide therapies in general, the emergence of resistance limits therapeutic efficacy.
U.S. Pat. No. 8,598,334 and WO 2012/145697 mention the use of antisense oligonucleotides to target HBV.
The control of viral infection needs a tight surveillance of the host innate immune system which could respond within minutes to hours after infection to impact on the initial growth of the virus and limit the development of a chronic and persistent infection. Despite the available current treatments based on IFN and nucleos(t)ide analogues, the Hepatitis B virus (HBV) infection remains a major health problem worldwide which concerns an estimated 350 million chronic carriers who have a higher risk of liver cirrhosis and hepatocellular carcinoma.
There is a need for new anti-viral therapies, in particular anti-HBV therapies. There is also a need to have a therapeutic strategy that enables one to target different types of HBV genotypes.